Changing Value in a Field Based on Condition

Good morning,

I know there are several ways to achieve what I'm attempting, but I can't seem to get any of them to work without messing up the rest of my data.  I have a field named "Company" in V_String format which contains 0 values.  Whenever there is a 0 in this field, I want to change this to "UNASSIGNED" without messing with any of my other Company values. 

I've tried Dynamic Replace, Switch, Conditional IF, etc.  Can anyone tell me the most logical way to do this without messing up the rest of my data?

Thanks!